1. Field of the Invention
The present invention relates to a bolometer that is an infrared sensor, and more particularly, to an infrared bolometer having a signal bridge used for reading a resistance value varied by infrared heat and removing the residual heat of a heat absorption layer.
2. Background of the Related Art
A bolometer that is a kind of infrared sensor absorbs infrared rays radiated from an object and converts the infrared rays into thermal energy, resulting in a temperature increase which varies an electric resistance. The bolometer measures the varied resistance to sense the object.
The bolometer is employed in both commercial and military fields. The bolometer is constructed in such a manner that an absorbent body for absorbing infrared heat of an object and a resistor whose resistance value is varied by the absorbed heat are separated from a substrate by a signal bridge.
FIG. 1 illustrates a conventional bolometer. Referring to FIG. 1, the bolometer includes a lower substrate 110, an upper substrate 120, and a signal bridge 130. The lower substrate has an integrated circuit built therein for reading a signal, the integrated circuit built being coated with a protection layer. The upper substrate 120 includes an absorbing layer (not shown) for absorbing infrared rays and a resistor (not shown) whose resistance value is varied by infrared heat absorbed by the absorbent. The upper substrate is spaced apart from the lower substrate 110 by a predetermined distance. The signal bridge 130 connects the upper and lower substrates to each other mechanically or electrically.
The bolometer having the aforementioned structure receives a resistance signal from the resistor of the upper substrate 120 through the signal bridge 130 and controls the resistance signal through the integrated circuit of the lower substrate 110 to sense the temperature of an external object.
To improve the performance of the bolometer, infrared heat radiated from the object must be absorbed without loss and residual heat must be completely removed after the signal is measured. In the conventional bolometer structure, the signal bridge 130 mechanically or electrically connects the upper substrate 120 to the lower substrate 110 and, simultaneously, removes residual heat after the signal is measured.
However, the signal bridge 130 is made of a metal material capable of transmitting an electric signal so that it can have high thermal conductivity. High thermal conductivity results in a loss of heat when the bolometer absorbs infrared heat.
To solve this problem, the signal bridge 130 is made long enough to reduce the thermal conductivity of the bolometer. However, there is a limitation in increasing the length of the signal bridge 130 because a pixel size is fixed.
Furthermore, for the conventional bolometer, heat stored in the resistor may not be completely removed after the signal is read although the length of the signal bridge 130 is increased to reduce the thermal conductivity. The residual heat contributes to an increase in the temperature of the resistor together with self-heating to thereby deteriorate the performance of the bolometer.